unicode: copy glyph to clipboard on cell click

Assume the only reason to click a cell is to copy the glyph contents, so
help the user by copying it automatically, avoiding the need for exact
selection and usually a copy command.

Should support Trident browsers out of the box, and Gecko with effort.
(At last a feature where the IE(>6) solution is vastly superior.)
Tested in MSIE 6.0/7.0 and Iceweasel 3.5.8/3.6.3 with XPCOM enabled.